The paper examines the behaviour of structural timber members subjected to axial compression or combined axial compression and bending. Based on experimental and numerical investigations, the accuracy of the existing approach in Eurocode 5 for the design of timber members subjected to axial compression or combined axial compression and bending is assessed and modifications are suggested. By means of extensive experimental investigations, a data base was created for the validation of calculation models and for the assessment of design concepts. In order to assess the behaviour of timber members subjected to axial compression or combined axial compression and bending, strain-based calculation models were developed.
The investigations indicate that the existing approach of Eurocode 5 based on 2nd order analysis can lead to an overestimation of the load-bearing capacity. Hence, a modified design approach was developed which agrees with the results of the Monte Carlo simulations very well and thus ensures a safe and economical design of timber members subjected to compression or combined compression and bending.
The mechanical behaviour of timber-to-timber connections with internal panels of densified veneer wood (DVW) and fibre-reinforced polymer (FRP) dowels was experimentally assessed and a design method, based on EN 1995-1-1, was developed. Embedment tests on DVW plates and bending/shear tests on FRP dowels were performed to characterise these components, followed by full-scale tests of connections assembled with these materials. The results show that these connections exhibit a mechanical behaviour compatible with structural applications, regarding both load-carrying capacity and ductility. The proposed design model is based on EN 1995-1-1’s expressions for connections with dowel-type fasteners and gives good predictions of the experimental load-carrying capacities.
In timber research, a main objective is the development and promotion of innovative and efficient timber structures. Therefore a pilot building, named ETH House of Natural Resources, has been designed, which uses two innovative structural systems, a post-tensioned timber frame and a composite beech LVL concrete floor. The building will be used as an office building for the Laboratory of Hydraulics, Hydrology and Glaciology from ETH Zürich and will serve as a showcase building of a sustainable and reliable timber construction for students and researchers, among others.
Cross-laminated timber (CLT) panels are relatively new engineered wood products that can be used as load bearing walls, floors and roof elements in innovative and high quality modern timber structures. The fire behavior of cross-laminated timber panels requires careful evaluation to allow the expansion of CLT elements usage in buildings. A University of British Columbia study has been conducted at the Trees and Timber Institute CNR-IVALSA in San Michele all’Adige, Italy to experimentally evaluate the fire performance of Canadian CLT panels. In total, ten loaded fire tests were performed using standard fire curves (ULC/ASTM and ISO) to study the influence of different cross-section layups on the fire resistance of floor and wall elements and to investigate the influence of different anchors on the fire behavior of wall elements. This paper presents the main results of the experimental analyses and discusses in particular the charring rate, one of the main parameters in fire design.
At the Institute of Structural Engineering (IBK) of ETH Zurich, the fire behaviour of timber-concrete composite slabs made with beech laminated veneer lumber (LVL) (BauBuche) was investigated. This composite slab is made of a thin plate (depth: 40 mm or 80 mm) using beech LVL and a concrete layer on top (depth: 160 mm or 120 mm). The beech plate acts both as formwork and as tensile reinforcement. This innovative slab system was implemented for the first time in the ETH House of Natural Resources at ETH Zurich. This paper summarizes the results of two largescale fire tests on loaded timber-concrete composite slabs exposed to standard ISO fire. Both fire tests show that the timber-concrete composite slab using beech LVL reaches sufficient fire resistance and integrity for 90 min and 60 min, respectively.
This research paper deals with the evaluation of the dynamic modal vibration tests conducted on an innovative timber structure, the ETH House of Natural Resources. The building serves as a demonstrator of several innovative structural systems and technologies relating to timber. The main load-bearing structure comprises a posttensioned timber frame, which was subjected to modal vibration tests, firstly in the laboratory and, subsequently on the construction site. In this paper, the modal characteristics (eigenfrequencies, damping ratios and mode shapes), obtained from the laboratory testing campaign are presented. The modal vibration data is evaluated using polynomial and subspace identification techniques. The obtained results reveal that the structure exhibits pure translational, beam and column modes, as well as mixed beam-column modes. The bottom connection of the columns delivers significant influence on the modal characteristics, whereas the level of post-tensioning force yields no substantial influence in the modal characteristics obtained from low amplitude modal vibration tests.
Fire safety is widely perceived as a barrier to implementation of tall timber buildings, particularly for engineered mass timber buildings with significant areas of exposed timber and timber structural framing. This negative perception is exacerbated by a lack of scientific data or experimental evidence on a range of potentially important issues that must be properly understood to undertake rational, performance-based engineering design of such structures. With the goal of delivering fully engineered structural fire designs, this paper presents and discusses a framework for using scientific knowledge, along with fire engineering tools and methods, to enable the design of timber buildings such that, when subject to real fire loads, their performance is quantified. The steps in this framework are discussed with reference to the available literature, in an effort to highlight areas where additional knowledge and tools are needed.
To estimate the loss of tendon force for a post-tensioned timber connection a series of tests are being conducted at the ETH in Zurich. Several post-tensioned specimens are being observed in different climate conditions. One set of specimens is in a climate chamber, where the relative humidity and temperature are kept constant. The second set of test specimens is positioned in an uncontrolled environment, where temperature and relative humidity change daily. The two environments allow estimating the influence of changes in relative humidity and temperature on the loss rate of tendon force. First results show that the relative humidity influences this rate, making it a key variable to estimate the total loss in post-tensioning force during the lifetime of a building.